Multi-level integrated photonic devices

ABSTRACT

A laser and electroabsorption modulator (EAM) are monolithically integrated through an etched facet process. Epitaxial layers on a wafer include a first layer for a laser structure and a second layer for an EAM structure. Strong optical coupling between the laser and the EAM is realized by using two 45-degree turning mirrors to route light vertically from the laser waveguide to the EAM waveguide. A directional angled etch process is used to form the two angled facets.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional under 35 U.S.C. 120 of U.S. applicationSer. No. 11/105,552, filed Apr. 14, 2005, now U.S. Pat. No. 7,656,922,which claims the benefit under 35 U.S.C. 119(e) of U.S. ProvisionalApplication No. 60/562,231, filed Apr. 15, 2004, entitled “Multi-LevelIntegrated Photonic Devices,” the disclosure of which is herebyincorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates, in general, to photonic devices, and moreparticularly to improved multi-level integrated photonic devices andmethods for fabricating them.

In the past, semiconductor lasers were typically fabricated by growingthe appropriate layered semiconductor material on a substrate throughMetalorganic Chemical Vapor Deposition (MOCVD) or Molecular Beam Epitaxy(MBE) to form an active layer parallel to the substrate surface. Thematerial was then processed with a variety of semiconductor processingtools to produce a laser cavity incorporating the active layer, andmetallic contacts were then attached to the semiconductor material.Finally, laser mirror facets were formed at the ends of the laser cavityby cleaving the semiconductor material to define edges or ends of alaser optical cavity so that when a bias voltage was applied across thecontacts, the resulting current flow through the active layer wouldcause photons to be emitted out of the faceted edges of the active layerin a direction perpendicular to the current flow.

An improvement over the foregoing process was described in U.S. Pat. No.4,851,368, which discloses a process for forming mirror facets forsemiconductor lasers by a masking and etching process that allowedlasers to be monolithically integrated with other photonic devices onthe same substrate. This patent also teaches thattotal-internal-reflection facets can be created within an optical cavitythrough the fabrication of such facets at angles greater than thecritical angle for light propagating within the cavity. The ability tofabricate multiple photonic devices on a single substrate led to thefabrication of complex integral optical circuits in which multipleactive and passive optical devices are integrally fabricated on a singlesubstrate. Such optical circuits may incorporate integrated lasers,waveguides, detectors, semiconductor optical amplifiers (SOA), gratings,and other optical devices.

Recently, there has been tremendous interest in developing anelectroabsorption-modulated laser (EML) through the integration of alaser and an electroabsorption modulator (EAM). However, existingmethods of fabricating monolithic EML devices typically have involvedsemiconductor regrowth steps to separately fabricate the laser and theEAM, but such methods have resulted in poor yields and high costs.

Copending U.S. patent application Ser. No. 10/226,076, filed Aug. 23,2002, entitled “Wavelength Selectable Device” and assigned to theassignee hereof, discloses a method of incorporating monolithicstructures such as an electroabsorption modulator coupled with a lasercavity on a substrate without the need for epitaxial regrowth.

Another example of an integrated EML device is described in U.S. Pat.No. 6,483,863, wherein the EML comprises two stacked asymmetricwaveguides, the first waveguide forming a laser and the second waveguideforming an EAM. The two waveguides support two different modes of lightpropagation and are arranged so that light propagating in the firstwaveguide is transferred into the second waveguide via a lateral taperin the first waveguide. However, due to the use of a lateral taper totransfer light propagating in the laser to the EAM waveguide, closeproximity of these two waveguides is required, resulting in a reducedconfinement factor for each quantum well in the laser.

A very important factor in determining laser performance is itsconfinement factor Γ for each quantum well in the laser. A smaller valueof Γ leads to higher threshold currents for lasing and results in ahigher amount of dissipated heat by the laser. Reducing heat dissipationby lasers is a key requirement of modern-day lasers and is veryimportant to a viable EML product. A modal analysis for a typical laserstructure including a metal contact layer on the top, or p-side of thelaser indicates a confinement factor Γ of 2.55% for each quantum well inthe laser. A modal analysis of a structure similar to that of U.S. Pat.No. 6,483,863, including both the laser and underlying EAM, but alsoincluding the p-side metals, results in a confinement factor of 1.37%due to the proximity of the EAM, which is required since theelectroabsorption modulated laser (EML) is formed by transferring lightpropagating in the laser waveguide to the EAM waveguide via a lateraltaper in the laser waveguide. The result is a laser device havingsuboptimal performance.

SUMMARY OF THE INVENTION

Briefly, the present invention is directed to improved integratedmultilayer photonic optical circuits and to an improved process forfabricating such circuits in multiple epitaxially grown layers on asubstrate. The optical circuits so fabricated are directly coupledthrough integrally formed etched mirrored facets to avoid the need forthe close proximity of the circuit components that is required for priorEML elements, thereby providing improved performance.

More particularly, the present invention is directed to a process forfabricating integrated photonic devices on a substrate through theetching of trenches downwardly along the z-axis of the devices but alsoat an angle to the x, y and z axes. In accordance with a preferred formof the present invention, the trenches are etched downwardly at an angleof 45 degrees to the x axis (along the length of the laser cavity) andat an angle of 10 degrees to the y-axis.

In the preferred form of the invention, multiple layer epitaxy is usedto provide an electroabsorption modulator structure on a substrate, andan optimized laser structure on the EAM structure. Vertically displacedlaser and EAM devices are fabricated in these structures, to form an EMLwafer wherein light travels parallel to the plane of the semiconductorsubstrate in both the laser and the EAM. To optically connect thesedevices, a first angled etched facet is fabricated to provide a firsttotal internal reflection at the output end of the laser to cause thelaser light to travel out of the laser cavity in a directionperpendicular to the plane of the semiconductor. A second angled etchedfacet is fabricated at the input end of the EAM to receive the lightfrom the laser and to thereby couple the two photonic devices. Adirectional angled etch process is used to form the two angled facets.

In the past, trenches have only been etched vertically downward, orvertically downward with an angle to only one direction, as taught, forexample, in U.S. Pat. No. 4,956,844. This patent describes an etchprocess for forming two total-internal-reflection facets, one at eachend of a linear laser cavity, with each facet being positioned at anangle of 45° with respect to the plane of the active layer so that lightpropagating in the laser cavity is directed perpendicularly upwardly atone facet, resulting in surface emission at that facet, while lightpropagating in the laser cavity is directed perpendicularly downwardlyat the other facet where it is directed to a high reflectivity stackbelow the laser structure.

In the present invention the facets, which function as turning mirrors,are fabricated in one Chemically Assisted Ion Beam Etching (CAIBE)procedure, by lithographically creating windows in an oxide etch-mask onthe EML wafer to define the location of the etch, and then positioningthe wafer at an angle to an incident ion beam while performing a deepetch to form trenches which define the facet surfaces. In accordancewith the preferred form of the present invention, the trenches areetched into the wafer downwardly along the z-axis of the device and alsoat an angle to the x-axis, along the length of the laser cavity, and atan angle to the y-axis, perpendicular to the x and z axes; for example,the trenches are etched at an angle of 45 degrees to the x-axis and 10degrees to the y-axis. The resulting 45-degree turning mirrors on thelaser and on the EAM device lie in parallel planes displaced from eachother by several micrometers and serve to efficiently couple the twooptical devices with essentially no detrimental effect on theconfinement factor of the laser in the presence of the adjacent EAMstructure.

BRIEF DESCRIPTION OF DRAWINGS

The foregoing, and additional objects, features and advantages of thepresent invention will be apparent to those of skill in the art from thefollowing detailed description of preferred embodiments thereof, takenwith the accompanying drawings, in which:

FIG. 1 shows a two layer epitaxial structure for use in fabricating anintegrated optical circuit incorporating a laser and anelectroabsorption modulator (EAM) in accordance with a preferredembodiment of the present invention;

FIG. 2 (a) illustrates a modal analysis for a laser without an EAMstructure underneath it;

FIG. 2( b) illustrates a modal analysis for a prior art waveguidestructure incorporating two stacked asymmetric waveguides;

FIG. 2( c) illustrates a modal analysis for a waveguide structure inaccordance with the present invention;

FIG. 3 is a diagrammatic, partial side elevation of an etched facetelectroabsorption-modulated laser (EML) optical circuit incorporating adownward-emitting laser and an integrated surface-receiving EAM,fabricated from the structure of FIG. 1 in accordance with theinvention;

FIG. 4 is a perspective view of the EML device of FIG. 3;

FIG. 5 is a diagrammatic, partial top view of the device of FIG. 4;

FIG. 6 is a top perspective view taken from the EAM end of the EML ofFIG. 3, illustrating the location and direction of angle-etched trenchesthat form the angled facets in the EML device of the invention;

FIG. 7 is a top perspective view taken from the laser end of the EML ofFIG. 3, illustrating the location and direction of angle-etched trenchesthat form the angled facets in the EML device of the invention; and

FIG. 8 is a top plan view of the EML of FIG. 3, illustrating thelocation and direction of angle-etched trenches that form the angledfacets in the EML device of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Turning now to a more detailed description of the invention, multipleintegrated photonic devices are fabricated on a wafer, or chip 10,illustrated in FIG. 1, to form an optical circuit with multiplefunctions to provide compact and cost-effective components for a varietyof applications. As illustrated, the wafer 10 includes two epitaxialstructures 12 and 14 on a common substrate 16, with the first structure12 being positioned on the substrate 16 and the second structure 14being positioned on top of the first structure. A buffer layer 18 may beincorporated between the two structures 12 and 14 to provide electricalisolation. Furthermore, the thickness of the buffer layer is chosen tooptically optimize both the laser and EAM structure. The epitaxialstructures 12 and 14, as well as buffer layer 18, are grown, forexample, in a single Metalorganic Chemical Vapor Deposition (MOCVD)growth, and no epitaxial re-growth is required for the device of thepresent invention. In the illustrated embodiment, the layers in thefirst structure are doped to cause it to function as a semiconductorelectroabsorption modulator (EAM), and the layers in the secondstructure are doped to produce a semiconductor laser. The EAM structureis epitaxially deposited on the substrate and the laser structure isthereafter epitaxially deposited on the EAM structure in the illustratedembodiment.

The structures on the substrate 16 may be formed, for example, from asuitably doped type III-V compound, or an alloy thereof. The EAMstructure 12 may be a succession of layers deposited by an epitaxialdeposition process such as Metalorganic Chemical Vapor Deposition(MOCVD). Typically, these layers may include the following layers on anInP substrate: p-doped InP buffer layer, p-doped InGaAs p-contact layer,p-doped InP transition layer, InGaAsP quantum wells and barriers,n-doped InP layer, and an n-doped InGaAs n-contact layer. The laserstructure 14 also may be a succession of layers, deposited by the MOCVDon the top surface of structure 12, to form an optical cavityincorporating an active region. Although many types of laser cavitiescan be fabricated in accordance with the invention, the invention willbe described herein in terms of ridge lasers, for convenience. As istypical for solid state ridge lasers, the structure 14 includes upperand lower cladding regions formed from lower index semiconductormaterial, for example InP, than is used in the central active region,which may be formed with In AlInGaAs-based quantum wells and barriers. Atransition layer of InGaAsP may be formed in addition to a p-dopedInGaAs contact layer on the top part of structure 14 to provide an ohmiccontact with a top metal layer, which is deposited on the structure 14,for connecting the laser to a bias source. The quantum wells in the EAMare designed to have a higher bandgap than the quantum wells in thelaser.

The structures 12 and 14 may share some of the deposited layers, so thatthe interface between the structures is common to both.

As discussed above, the confinement factor Γ for each quantum well in alaser is a very important factor in determining laser performance. Asmaller value of Γ leads to higher threshold currents for lasing andresults in a higher amount of dissipated heat by the laser. Reducingheat dissipation by lasers is a key requirement of modern-day lasers andis very important to a viable EML product. A modal analysis for atypical laser structure, for example a laser similar to that describedin U.S. Pat. No. 6,483,863, without the presence of an EAM underneathbut including a metal contact layer on the top, or p-side of the laser,is illustrated by graph 20 in FIG. 2( a). In this analysis, variationsin the index of refraction of the laser are illustrated by curve 22,while the corresponding modal intensity is indicated by curve 24. Theresulting confinement factor Γ for each quantum well in this laser is2.55%.

A modal analysis of a structure similar to that of U.S. Pat. No.6,483,863, including both the laser and the underlying EAM, and alsoincluding the p-side metals, gives rise to the solution shown by graph26 in FIG. 2( b), wherein curve 28 illustrates variations in the indexof refraction of the laser and curve 30 indicates correspondingvariations in modal intensity. In this illustration the Γ is reduced to1.37%, due to the required proximity of the EAM, the proximity betweenthe laser and the EAM being required since the electroabsorptionmodulated laser (EML) is formed by transferring light propagating in thelaser waveguide to the EAM waveguide via a lateral taper in the laserwaveguide.

A modal analysis of an EML device constructed in accordance with thepresent invention is illustrated by graph 32 in FIG. 2( c). As will bedescribed in detail below, this device does not require the sameproximity of the laser and EAM as is required in devices such as thosedescribed in U.S. Pat. No. 6,483,863 in order to attain the desiredoptical coupling. Therefore, improved confinement of the laser isattained by inserting a buffer between the laser and the EAM layer. Thisis accomplished, for example, by providing an additional thickness of 2μm in the bottom cladding layer of the laser. In the modal analysis ofsuch a device in FIG. 2( c), curve 34 illustrates the index ofrefraction of the laser, while curve 36 illustrates the correspondingmodal intensity for the laser of the invention. This results in aconfinement factor of 2.55%. As shown by this analysis, there isessentially no detrimental impact on the Γ of the laser due to thepresence of the EAM underneath, and there is essentially no degradationin the performance of either the laser or the EAM for devicesconstructed in accordance with the invention.

Turning now to a more detailed description of the invention, an EMLdevice 40, which is fabricated in the wafer 10 of FIG. 1, is illustratedin the diagrammatic partial side view of FIG. 3 and in the topperspective view of FIG. 4, to which reference is made. The EML 40 isbased on a design incorporating a laser structure 42 in layer 14 that isvertically displaced from an EAM structure 44 formed in layer 12. Asillustrated, the downward-emitting laser 42 is a ridge-type laser havingan optical cavity, or waveguide, that includes an active region 46 and aridge 48 covered by a top electrode layer 50. At its output end thelaser includes an upper turning mirror 52 which is a totally internallyreflective facet at an angle of about 45° with respect to thelongitudinal axis, or x axis, 54 of the laser and also at a 45° anglewith respect to the vertical z axis of the device. At the opposite endof the laser are suitable filters 60 and a monitoring photodetector 62that terminates in a facet 64 at the Brewster angle. Such a surfaceemitting laser is described in detail in copending U.S. application Ser.No. 10/958,069, filed Oct. 5, 2004, entitled “Surface Emitting andReceiving Photonic Device”, and assigned to the assignee hereof, thedisclosure of which is hereby incorporated herein by reference. In thepreferred form of the invention, the buffer layer 18 is an extension, orthickening, of the cladding layer which is a part of the laserstructure, as described above. The laser is fabricated in the layer 14by masking and etching techniques known in the art.

The surface-receiving EAM 44 is a ridge-type device fabricated in layer12 of the wafer, again by known masking and etching techniques, andincorporates an optical cavity, or waveguide, having a ridge portion 60and an active region 62. An electrode layer 64 is placed on the topsurface of the EAM structure for the application of a modulatingvoltage. The input end of the EAM structure includes a second, or lower,turning mirror 66 which consists of a totally internally reflectingfacet at an angle of about 45° to the x axis 54 and to the vertical zaxis of the device. The EAM mirror 66 is below, vertically aligned with,and substantially parallel to the upper laser mirror 52, so that lightpropagating in the laser is deflected by mirror 52 and is emitted fromthe bottom surface of the laser. The emitted light is directed onto theEAM device, where it is directed by mirror 66 along the axis of the EAMcavity. As will be described below, both the mirror 52 and the mirror 66are also at an angle of about 10° with the y axis to facilitate thefabrication of the device.

Strong optical coupling between the laser and the EAM is provided by thetwo 45-degree turning mirrors 52 and 66. A bias voltage (not shown) isapplied to an electrode layer 50 on the top surface of the laser, inknown manner, to cause laser light to propagate in the laser cavity.This light propagates horizontally in the laser cavity until it impingeson the 45-degree etched facet 52, where total internal reflection occursand causes the downward-emission from the laser. In effect, thedirection of the laser beam is changed by 90 degrees. Then another 45degree etched facet causes the laser beam to be changed by another 90degrees and directs it into the EAM. Angles other than 45 degrees canalso be used; however, angles above the critical angle are preferred toallow total internal reflection.

The perspective view of FIG. 4 and the top plan view of FIG. 5illustrate the EML structure 40 described above without the underlyingsubstrate, for clarity, and also illustrate the output end 70 of the EAMstructure. As shown, the EAM preferably incorporates a partiallyemissive output facet 72 that emits a portion of the received light as amodulated light beam 74 and reflects the remaining light into a foldedcavity portion 76. The cavity portion is terminated at its distal end bya facet 78, which is at the Brewster angle to prevent internalreflection. An EAM structure where back reflection is minimized by theprovision of a facet at or near the Brewster angle at the distal end isdescribed in copending U.S. patent application Ser. No. 10/802,734,filed Mar. 18, 2004, assigned to the assignee hereof, the disclosure ofwhich is hereby incorporated herein by reference.

The laser 42 is fabricated to produce single-longitudinal-mode behavior,and for this purpose preferably makes use of etalons, as taught incopending U.S. patent application Ser. No. 10/929,718, filed Aug. 31,2004, entitled “Single Longitudinal Mode Laser Diode” and assigned tothe assignee hereof, the disclosure of which is hereby incorporatedherein by reference. Etalons are introduced in the laser and EAMstructures to modify the optical behavior and to provide electricalisolation. The preferred location of these etalons for electricalisolation is in the proximity of the two turning mirrors. However, thesingle-longitudinal-mode behavior can be obtained by a variety ofdifferent structures, known to experts in the field, one such examplebeing a distributed feedback (DFB) laser.

In accordance with the present invention, etched trenches that extenddownward along, and at an angle to, the z-axis of the EML devicedescribed above and also extend at an angle to both the x-axis andy-axis of the device are used to fabricate the upper and lower turningmirrors so that they lie in parallel, closely spaced planes in verticalalignment with each other. In the past, trenches have only been etchedvertically downward, or vertically downward with an angle to only onedirection, as taught, for example, in U.S. Pat. No. 4,956,844. In thatpatent, an etch process forms two total-internal-reflection facets, oneat each end of a linear laser cavity, with each facet being positionedat an angle of 45° with respect to the plane of the active layer. Inthat device, light propagating in the laser cavity is directedperpendicularly upwardly at one facet, resulting in surface emission atthat facet, while the second facet, at the other end of the cavity,directs the light perpendicularly downwardly to a high reflectivitystack below the laser structure. In the present invention, however,parallel facets are fabricated by etching trenches along the directionof the z axis of the device and at angles to the x, y and z axes.

A preferred process for fabricating the upper and lower facets of theEML device 40 is illustrated in FIGS. 6-8, to which reference is nowmade. In each of these Figures, the EML device 40 of the precedingFigures is illustrated, with an imaginary plane 90 being included forreference purposes. This plane 90 is located at the level of the top ofthe laser structure 42, corresponding to the surface of the wafer, andis parallel to the surface of the substrate and to the active layers ofthe laser and EAM structures. The z axis of the plane is perpendicularto the plane and to the surface of the wafer; the x-axis of the plane 90is parallel to the x-axis 54 of the laser (FIG. 3); and the y-axis ofthe plane is mutually perpendicular to the x and z axes, as illustratedin the Figures.

In accordance with the preferred process, the facets 52 and 66 areformed by etching two parallel trenches 92 and 94 in the wafer, usingsuitable masking, with a directional etch such as a CAIBE etch. In afirst masking step, apertures 96 and 98 are formed on the wafer surfaceat locations corresponding to those shown on the plane 90. The surfaceof the wafer 10 is coated with a mask material, such as SiO₂, andphotolithography followed by reactive ion etching (RIE) is performed todefine the apertures 96 and 98 in the mask. The wafer is then etched ina chemically assisted ion beam etcher (CAIBE) by positioning the sampleso that the ion beam is directed downwardly, generally in the directionof the z axis but also at angles to it and to the x and y axes. Theapertures face toward the ion beam and the sides of the trenches 92 and94 are then formed parallel to the ion beam. After this step, SiO₂ isdeposited and photolithography followed by RIE and CAIBE are performedto form the vertical facets such as 64, 72, and 56. Facet 56 ispreferably positioned between section 52 and the EAM 44. In the case ofa DFB laser, facet 56 can be eliminated. The ridge structure is definedand metallizations added to provide a functional EML.

The trenches are etched downwardly, generally along the z-axis but at a45° angle to that axis, and also at a 45° angle to the plane of the x-yaxes and thus also to the x-axis. In the example illustrated here, thetrenches are also etched at a 10° angle to the y-axis. The etchedtrenches extend the width of the corresponding apertures 96 and 98 inorder to extend across the desired width of the turning mirrors 52 and66, and extend only as deep as is required to form the mirror surfaces.As discussed above, the turning mirrors are fabricated in one CAIBEprocess step, by lithographically creating the apertures 96 and 98 in anoxide etch-mask to define the location of the etch and then positioningthe wafer at an angle to the incident ion beam. The 45-degree turningmirrors 52 and 66 are to lie in parallel planes displaced from eachother by several micrometers. The trenches 92 and 94 intersect with theplane 90 at the surface of the wafer at the respective apertures 96 and98. Parallel lines aa′ and bb′ illustrated in plane 90 in FIG. 8,identify the sides of the apertures 98 and 96, respectively. Line cc′ inFIG. 8 is parallel to bb′ and defines the other side of aperture 96, asshown in FIG. 8. A line drawn from the center of the upper 45-degreeturning mirror 52 to any point on the line aa′ determines the locationof the oxide mask window 98, and also determines the compound angle atwhich the wafer must be oriented relative to the incident ion beamduring the CAIBE etch. Similarly, the location of the oxide mask window96 for etching the lower turning mirror is determined by theintersection of a line extending from the center of the lower turningmirror 66 at the same compound angle, with the line cc′ in the surface90. The particular compound angle used for the CAIBE etch is acompromise between two design parameters: maximizing the overlap of thepropagating optical mode and the surface area of the turning mirror, andminimizing the etch depth of the CAIBE etch.

Although lines aa′, bb′ and cc′ have been shown to be straight, it willbe understood that these lines may be curved. Furthermore, althoughlines aa′ and bb′ are shown to be parallel, they may deviate from beingparallel.

Although the EML structure is illustrated with a downward-emitting laserand with an EAM that is surface-receiving, it will be understood that anupward surface-emitting laser could also be coupled with adownward-receiving EAM using the process described herein.

Although the present invention has been illustrated in terms ofpreferred embodiments, it will be understood that variations andmodifications may be made without departing from the true spirit andscope thereof as set out in the following claims.

1. A method of fabricating a semiconductor photonic device havingmutually perpendicular x, y, and z axes, comprising: providing asubstrate having an x-axis and a y-axis defining a plane along a surfaceof said substrate and a height defining a z-axis of said substrate;depositing a multilayer epitaxial structure on said substrate, saidmultilayer epitaxial structure containing a first and second waveguidestructures for said photonic device, at least one of said first andsecond waveguide structures having a longitudinal axis parallel to saidx-axis of said substrate, and said second waveguide structure beinglocated above said first waveguide structure; and etching at least afirst trench downwardly through a to surface of said multilayerepitaxial structure with a component along a z-axis of said substrate,said first trench being etched at non-perpendicular angles to both saidx- and y-axes of said substrate and having a side that passes across afirst one of said first and second waveguide structures at anon-perpendicular angle to the y axis and thereby forms a reflectivefacet defining a distal end of said first one of said first and secondwaveguide structures that reflects light toward a second one of saidfirst and second waveguide structures.
 2. The method of claim 1, whereinsaid etching is by Chemically Assisted Ion Beam Etching (CAIBE).
 3. Themethod of claim 1, wherein said first one of said waveguide structuresacross which said trench is etched includes a first, a second and athird layer, wherein said first layer is a lower cladding layer, saidsecond layer is an active layer, and the third layer is an uppercladding layer, said first trench being etched into said second andthird layers.
 4. The method of claim 3, wherein said semiconductorphotonic device includes a laser.
 5. The method of claim 4, wherein saidlaser is a DFB laser.
 6. The method of claim 5, wherein said etching isby CAIBE.
 7. A method of fabricating a semiconductor photonic devicehaving mutually perpendicular x, y, and z axes, comprising: providing asubstrate having an x-axis and a y-axis defining a plane along a surfaceof said substrate and a height defining a z-axis of said substrate;depositing a first Electroabsorption modulator (EAM) epitaxial structureon said substrate, said EAM epitaxial structure containing a firstwaveguide structure for an EAM in said photonic device, said firstwaveguide structure being elongated parallel to said x-axis of saidsubstrate; depositing a laser epitaxial structure on said first EAMepitaxial structure, said laser epitaxial structure containing a secondwaveguide structure for a laser in said photonic device, said secondwaveguide structure being elongated parallel to said x-axis of saidsubstrate; and etching at least a first trench downwardly into saidlaser epitaxial structure with a component along a z-axis of saidsubstrate, said first trench being etched at non-perpendicular angles toboth said x and y axes of said substrate.
 8. The method of claim 7,wherein said first trench is also etched into said EAM epitaxialstructure.
 9. The method of claim 8, wherein said etching is by CAIBE.10. The method of claim 7, wherein said laser is a single longitudinalmode laser.
 11. The method of claim 10, further comprising etching atleast a second trench downwardly into said laser epitaxial structure andsaid EAM epitaxial structure with a component along a z-axis of saidsubstrate, said second trench being etched at non-perpendicular anglesto both x- and y-axes of said substrate.
 12. The method of claim 11,wherein said first trench forms a first facet that provides totalinternal reflection for the laser light impinging upon it.
 13. Themethod of claim 12, wherein said second trench forms a second facet thatprovides total internal reflection for laser light impinging upon it anddirecting it to said EAM.
 14. The method of claim 13, wherein saidetching is by CAIBE.
 15. The method of claim 13, wherein said EAMfurther comprises a partially emitting output facet.
 16. The method ofclaim 15, wherein said EAM further comprises a facet terminating at adistal end.
 17. The method of claim 16, wherein said facet at saiddistal end is positioned at a Brewster angle to prevent back reflection.18. The method of claim 1, further comprising etching at least a secondtrench through said top surface of said multilayer epitaxial structure.19. The method of claim 1, wherein said reflective facet provides totalinternal reflection for light impinging upon it.
 20. The method of claim2, wherein said etching is carried out by first forming a mask on saidtop surface of said multilayer epitaxial structure; forming an aperturein said mask defining a shape of said trench and a location on said topsurface where said trench is to begin; and, directing said ion beam downthrough said aperture into said multilayer epitaxial structure at saidnon-perpendicular angle with respect to each of said x and y axes. 21.The method of claim 6, wherein said etching is carried out by firstforming a mask on said top surface of said multilayer epitaxialstructure; forming an aperture in said mask defining a shape of saidtrench and a location on said top surface where said trench is to begin;and, directing said ion beam down through said aperture into saidmultilayer epitaxial structure at said non-perpendicular angle withrespect to each of said x and y axes.
 22. The method of claim 9, whereinsaid etching is carried out by first forming a mask on a top surface ofsaid epitaxial structure; forming an aperture in said mask defining ashape of said trench and a location on said top surface where saidtrench is to begin; and, directing said ion beam down through saidaperture into said epitaxial structure at said non-perpendicular anglewith respect to each of said x and y axes.
 23. The method of claim 14,wherein said etching is carried out by first forming a mask on a topsurface of said laser epitaxial structure; forming first and secondapertures in said mask each defining a shape of said first and secondtrenches, and first and second locations on said top surface where saidfirst and second trenches are to begin, respectively; and, directingsaid ion beam down through said first and second apertures into saidepitaxial structure at said non-perpendicular angle with respect to eachof said x and y axes.